U.S. Pat. No. 6,318,522 B1 to Johnston et al. discloses a rotary damper with magnetic seals. A chamber is filled with magnetorheological fluid such that when the rotor is moved in the chamber the magnetorheological fluid damps the movement of the rotor. The magnetorheological fluid includes a fine iron powder or fine iron alloy particles suspended in a mineral oil or silicone. According to the '522 patent, the suspension of the particles in a fluid medium is known to affect the rheology of the medium in which the particles are suspended particularly when the fluid is subjected to a magnetic flux. Further, according to the '522 patent the fluid has one or more additives which prevent the iron from separating out from the fluid. See, col. 3, lns. 38 et seq.
Still referring to the '522 patent, magnets are placed in proximity to surfaces which rotate with respect to one another. The viscosity of the fluid increases in the presence of a magnetic field and the increased viscosity restricts the flow of fluid in gaps. According to the '522 patent it is believed that the iron particles in the magnetorheological fluid align which increases the viscosity of the fluid. The increased viscosity increases shear strength that any fluid must overcome in order to flow through the gaps.
U.S. Pat. No. 5,598,908 to York et al. discloses a fluid coupling device utilizing a magnetorheological fluid having a controllable yield strength in shear in response to a magnetic field.
U.S. Pat. No. 6,340,080 to Carlson discloses that a significant shear force for resisting relative movement can be obtained with a small amount of controllable medium, such as MR fluid, contained in the working space between movable members.
U.S. Pat. No. 6,371,267 B1 to Kao et al. discloses a magnetorheological fluid clutch. U.S. Pat. Nos. 5,779,013 and 5,845,753 to Bansbach disclose torque transfer apparatuses using magnetorheological fluid. U.S. Pat. No. 6,527,661 B2 to Leeper discloses a limited slip differential having a magnetorheological fluid brake.
It is desirable for a magnetorheological device to be capable of high torsional loads. The invention as disclosed below satisfies this and other needs.